Methods and device for controlling an internal combustion engine

ABSTRACT

A first method is for determining a variable, which characterizes a fuel injection, in an internal combustion engine of a motor vehicle in a hot-start situation wherein fuel is injected directly into at least one combustion chamber from a high-pressure region of a fuel supply system; the variable, which characterizes the injection quantity, is corrected at least in dependence upon a variable which represents a temperature of the fuel. A second method is for determining a hot-start situation in an internal combustion engine of a motor vehicle wherein a hot-start situation is determined at least based on a variable, which represents a temperature of the fuel, and based on a fuel pressure. The invention relates likewise to corresponding arrangements, a corresponding control apparatus for an internal combustion engine, a corresponding computer program having program-code means and a corresponding computer program product having program-code means.

RELATED APPLICATIONS

This application is the national stage of international applicationPCT/DE 01/04659, filed Dec. 11, 2001, designating the United States andclaiming priority from German patent application No. 100 64 653.0, filedDec. 22, 2000, the entire content of which is incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to a method for determining a variable, whichcharacterizes an injection quantity, in an internal combustion engine ofa motor vehicle in a hot-start situation. The invention also relates toa method for determining a hot-start situation in an internal combustionengine of a motor vehicle. The invention likewise relates to thefollowing: corresponding arrangements, a corresponding control apparatusfor an internal combustion engine, a corresponding computer programhaving computer-code means and a corresponding computer program producthaving program-code means.

BACKGROUND OF THE INVENTION

Generally, a hot-start situation is meant when, for example, after ashort operating pause, a renewed start takes place in an internalcombustion engine which is still hot. In a hot engine at rest, fuelvapor bubbles form in the fuel line as well as in the injection valveitself. In the next start operation, these fuel vapor bubbles thenhinder the regular metering of fuel.

For this reason, an extended injection signal is, for example, outputtedunder hot-start conditions so that a certain minimum quantity of fuelcan be made available for the injection process even when there is anoccurrence of the fuel vapor bubbles.

German patent publication 4,039,598 discloses a hot-start method and ahot-start arrangement for an internal combustion engine. A hot-startsituation is then assumed in accordance with the teaching presentedthere when the engine temperature as well as the intake air temperatureexceed specific threshold values and, furthermore, the difference inmagnitude between the intake-air temperature at an earlier time pointand the intake-air temperature at a new start lies above a selectablethreshold.

German patent publication 4,435,419 discloses a control system formetering fuel to an internal combustion engine. Here, a hot-startsituation is assumed and a corresponding hot-start bit is set when theengine temperature exceeds a first threshold value and, in addition, anincrease of the intake air temperature by a specific amount has takenplace since the last measurement. The last value can be that value whichwas present at the time point of switching off the engine and the newvalue can be obtained at the time point of switching on the ignition orthe starter. The hot-start bit remains set until the engine temperaturehas dropped below a second threshold value or until a predeterminedtotal air mass has flown through the intake manifold. The last-mentionedtotal air mass is determined by means of an integration of the signal ofan air-mass sensor in the intake manifold.

A method and an arrangement for controlling the metering of fuel in aninternal combustion engine are known from German patent publication 19547 644. Here, the fuel quantity, which is to be injected, is correctedin dependence upon the temperature, the density and the pressure of thefuel. The method of German patent publication 195 47 644 is preferablyutilized in self-igniting internal combustion engines which are equippedwith a common rail system.

Especially in modern fuel injection systems (which systems operate witha high-pressure fuel injection), some components become hot such as thehigh-pressure pump even after switching off the engine whereby increasedtemperature values can occur compared to the switch-off temperature. Fora subsequent hot-start situation, the correct metering of fuel is ofspecial significance so that a certain and reliable start is ensured. Anessential aspect is also the hot-start recognition itself.

SUMMARY OF THE INVENTION

The invention is based on the task to improve the determination of avariable, which characterizes an injection quantity, in an internalcombustion engine of a motor vehicle in a hot-start situation as well asto improve the determination of a hot-start situation in an internalcombustion engine of a motor vehicle.

The task is solved, on the one hand, by a method for determining avariable, which characterizes an injection quantity, in an internalcombustion engine of a motor vehicle in a hot-start situation. Fuel froma high-pressure region of the fuel supply system is injected directlyinto at least one combustion chamber. The variable, which characterizesthe injection quantity, is corrected in the hot-start situation. Thevariable, which characterizes the injection quantity, is corrected atleast in dependence upon a variable representing a temperature of thefuel.

In this way, in fuel supply systems having high-pressure injection, thetemperature of the fuel when metering the fuel is considered in anadvantageous manner which leads to an improved start performance andcombustion performance in the hot-start situations.

Embodiments of the invention provide that the variable, whichcharacterizes the injection quantity, is an injection duration and thatthe variable, which represents the temperature of the fuel, is an enginetemperature or a coolant temperature and that a hot-start situation isdetermined based on the variable, which represents the temperature ofthe fuel, and a fuel pressure.

With these embodiments of the invention, the temperature and thepressure of the fuel are considered in an advantageous manner in themetering of fuel so that it is ensured in a hot start that thedetermined fuel quantity is metered. This leads to an especiallycultivated start performance of the engine with simultaneously reducedexhaust-gas emissions. It is especially advantageous to determine thefuel pressure in the high-pressure range of the fuel supply systemwhereby the pressure, which acts directly on the fuel to be injected, isconsidered in the metering of the fuel.

A preferred embodiment of the method provides that a hot-start situationis detected when an engine temperature or a coolant temperature exceedsan applicable temperature threshold value and the fuel pressure in thehigh-pressure range drops below an applicable pressure threshold value.

In this way, and especially for fuel supply systems having high-pressureinjection, a hot-start situation is reliably detected and the fuelquantity can be correspondingly metered because of the correction of theinjection duration.

The temperature of the fuel can be advantageously determined incorrespondence to a model and/or an applicable characteristic field ofthe engine temperature or coolant temperature. Furthermore, a criticaltemperature can be determined based on the fuel pressure in thehigh-pressure region of the fuel supply system and/or be taken from anapplicable characteristic field. By means of the determined fueltemperature and the critical temperature, a hot-start situation can beespecially advantageously detected in that the temperature of the fuelexceeds the critical temperature.

The task is further solved with a method for determining a hot-startsituation in an internal combustion engine of a motor vehicle wherein ahot-start situation is determined at least based on a variable, whichrepresents a temperature of the fuel, and based on a fuel pressure. Withthis measure, a hot-start situation in motor vehicles can be determinedespecially easily, rapidly and reliably.

The task is further solved with an arrangement for determining avariable, which characterizes an injection quantity, in an internalcombustion engine of a motor vehicle in a hot-start situation. Fuel froma high-pressure region of the fuel supply system is injected directlyinto at least one combustion chamber. The variable, which characterizesthe injection quantity, is corrected in the hot-start situation. Meansare provided with which the variable, which characterizes the injectionquantity, can be corrected at least in dependence upon a variable whichrepresents a temperature of the fuel.

The task is further solved with an arrangement for determining ahot-start situation in an internal combustion engine of a motor vehicle.Means are provided with which a hot-start situation can be determinedbased on a variable, which represents a temperature of the fuel, andbased on a fuel pressure.

Of special significance is the realization of the method of theinvention in the form of a control apparatus for an internal combustionengine, especially, of a motor vehicle. Here, means are provided forcarrying out the steps of the above-described methods.

Of special significance are further the realizations in the form of acomputer program having program-code means and in the form of a computerprogram product having program-code means. The computer programaccording to the invention includes program-code means in order to carryout all steps of the method of the invention when the program is carriedout on a computer, especially on a control apparatus for an internalcombustion engine of a motor vehicle. In this case, the invention isrealized by a program stored in the control apparatus so that thiscontrol apparatus, which is provided with the program, defines theinvention in the same way as the method. The computer program product ofthe invention includes program-code means which are stored on acomputer-readable data carrier in order to carry out the method of theinvention when the program product is executed on a computer,especially, on a control apparatus for an internal combustion engine ofa motor vehicle. In this case, the invention is realized by a datacarrier so that the methods of the invention can be carried out when theprogram product or the data carrier is integrated into a controlapparatus for an internal combustion engine, especially, of a motorvehicle. As a data carrier or as a computer program product, an electricstorage medium can especially be applied, for example, aread-only-memory (ROM), an EPROM or also an electric permanent memorysuch as a CD-ROM or DVD.

Further features, application possibilities and advantages of theinvention will become apparent from the following description of theembodiments of the invention which are shown in the following figures.All described embodiments or illustrated features themselves or in anydesired combination define the subject matter of the inventionindependently of their formulation or their illustration in the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an arrangement of the invention; and,

FIG. 2 shows a method of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, an internal combustion engine 1 is shown wherein a piston 2is movable back and forth in a cylinder 3. The cylinder 3 is providedwith a combustion chamber 4 to which an intake manifold 6 and anexhaust-gas pipe 7 are connected via valves 5. Furthermore, an injectionvalve 8 and a spark plug 9 are connected to the combustion chamber 4.The injection valve 8 is driveable by a signal TI and the spark plug 9is driveable by a signal ZW. The signals TI and ZW are transmitted by acontrol apparatus 16 to the injection valve 8 and the spark plug 9,respectively. The signal TI defines the injection signal and the signalZW the ignition angle. The injection valve is supplied with fuel by afuel high-pressure store 19 (for example, a common rail) via ahigh-pressure line 18. A pressure sensor 20 and a temperature sensor 21are mounted in the fuel high-pressure store 19 and transmit a pressuresignal P and a temperature signal T to the control apparatus 16. Ahigh-pressure pump moves the fuel from a low-pressure region into thehigh-pressure region of the fuel high-pressure store 19 and is not shownin the illustration of FIG. 1.

The intake manifold 6 is provided with an air-mass sensor 10 and theexhaust-gas pipe 7 is provided with a lambda sensor 11. The air-masssensor 10 measures the air mass of the fresh air supplied to the intakemanifold 6 and generates a signal LM in dependence thereon. The lambdasensor 11 measures the oxygen content of the exhaust gas in theexhaust-gas pipe 7 and generates a signal lambda in dependence thereon.The signals of the air-mass sensor 10 and the lambda sensor 11 aresupplied to the control apparatus 16.

A throttle flap 12 is accommodated in the intake manifold 6 and itsrotational position is adjustable by means of a signal DK. Furthermore,the exhaust-gas pipe 7 can be connected to the intake manifold 6 via anexhaust-gas recirculation line (not shown). The control of theexhaust-gas recirculation can, for example, take place via anexhaust-gas recirculation valve which is likewise not shown and can bedriven by the control apparatus 16.

In a first mode of operation, the homogeneous operation of the engine 1,the throttle flap 12 is partially opened or closed in dependence uponthe desired supplied air mass. The fuel is injected by the injectionvalve 8 into the combustion chamber 4 during an induction phase causedby the piston 2. The injected fuel is swirled by the simultaneouslyinducted air and is distributed essentially uniformly/homogeneously inthe combustion chamber 4. Thereafter, the air/fuel mixture is compressedduring the compression phase in order to then be ignited by the sparkplug 9. The piston 2 is driven by the expansion of the ignited fuel.

In a second mode of operation, the stratified mode of operation of theengine 1, the throttle flap 12 is opened wide. The fuel is injected intothe combustion chamber 4 during a compression phase caused by the piston2. Then, with the aid of the spark plug 9, the fuel is ignited so thatthe piston 2 is driven in the following work phase by the expansion ofthe ignited fuel.

In stratified operation as in homogeneous operation, a rotationalmovement is imparted to a crankshaft 14 by the driven piston via whichfinally the wheels of the motor vehicle are driven. A toothed wheel ismounted on the crankshaft 14 whose teeth are scanned by an rpm sensor 15mounted directly opposite the toothed wheel. The rpm sensor 15 generatesa signal from which the rpm (n) of the crankshaft 14 is determined andtransmits this signal (n) to the control apparatus 16.

The fuel mass, which is injected into the combustion chamber instratified operation and in homogeneous operation, is controlled (openloop and/or closed loop) by the control apparatus 16 especially in viewto a reduced fuel consumption and/or to a reduced development of toxicsubstances. The determination according to the invention of a hot-startsituation as well as the determination of the injection duration in ahot-start situation take also place in the control apparatus 16. Forthis purpose, the control apparatus 16 is provided with a microprocessorwhich has a program code stored in a memory medium which is suitable toexecute the total control (open loop and/or closed loop) of the engine1.

Input signals are applied to the control apparatus 16 and defineoperating variables of the engine measured by means of sensors. Forexample, the control apparatus 16 is connected to the following: theair-mass sensor 10, the lambda sensor 11, the rpm sensor 15, thepressure sensor 20 and the temperature sensor 21. Furthermore, thecontrol apparatus 16 is connected to an accelerator pedal sensor 17which generates a signal FP which indicates the position of anaccelerator pedal, which is actuable by a driver, and thereforeindicates the torque requested by the driver. An engine temperaturesignal is supplied as an additional input signal (not shown in FIG. 1)to the control apparatus 16. This input signal can, for example, be thesignal of a cooling water temperature sensor, an oil temperature sensoror even a component temperature sensor mounted on the engine block. Thecontrol apparatus 16 generates output signals with which, via actuators,the performance of the engine 1 can be influenced in correspondence tothe desired control (open loop and/or closed loop). For example, thecontrol apparatus 16 is connected to the injection valve 8, the sparkplug 9 and the throttle flap 12 and generates the signals TI, ZW and DKrequired for the control of the injection valve, spark plug and throttleflap.

The method according to the invention is implemented by the controlapparatus 16 and is explained in greater detail hereinafter.

Basically, a vapor bubble formation in the fuel supply system occurswith conventional fuels starting with temperatures above 100° C. and atsystem pressures of approximately 3 to 4 bar. In modern engines (whichare provided with a high-pressure fuel injection, for example, agasoline direct injection), no high pressure is available in the fuelsupply system as a rule at the start of the engine. Because of thenon-presence of the high pressure in start situations, it can sometimeshappen that a hot-start situation is present because of the overheatingof the fuel caused by the components of the fuel supply system which arestill hot. As a rule, after switching off the engine, it can occur thatthe temperature of the fuel (which is disposed in the injection systemand in the fuel supply system, especially in the common rail) canincrease in temperature for approximately 10 minutes longer until thetemperature of the fuel starts to drop. Because of this temperatureincrease after switching off the motor vehicle, a vapor bubble formationcan occur in the fuel system after switching off the vehicle whichleads, in a new-start situation, to a hot start.

FIG. 2 shows an embodiment of the method of the invention. The method ofthe invention starts with step 201. In this step, for example, theinitializations, which are required in the control apparatus, can takeplace for carrying out the method of the invention. In a next step 202,the fuel pressure in the fuel high-pressure store 19 is measured. Thiscan take place, for example, with a pressure sensor 20. In step 203,which follows step 202, the temperature of the engine is determined. Forthis purpose, the temperature of a fluid in the engine is, as a rule,measured. Preferably, the coolant temperature of the engine is appliedas the engine temperature. Alternatively, it is, however, also possibleto use a special component temperature sensor which is mounted in theregion of the cylinder head. In the ideal case, which, however, does notoccur in practice because of cost reasons, the fuel temperature can bemeasured directly in the high-pressure store 19 with a correspondingtemperature sensor 21.

After the completed engine temperature determination in step 203, thefuel temperature is computed in step 204 based on a model. In thesimplest case, it can be assumed in this model that the fuel temperaturediffers by a constant offset from the engine temperature, for example,5°. Here, the fuel temperature would correspond to the enginetemperature less an offset value. As an alternative, the determinationof the fuel temperature can be made based on a characteristic fieldstored in the control apparatus. Such a characteristic field can containadditional parameters in addition to the engine temperature, such as theshut-off duration of the motor vehicle, the ambient temperature of themotor vehicle, specific data of the used coolant or also data specificto the fuel.

In step 205 which follows step 204, a critical temperature is determinedin correspondence to the measured fuel pressure and the previouslydetermined fuel temperature. Here, the critical temperature is formedprimarily in dependence upon the fuel pressure. Here also, thepossibilities result that the critical temperature can be determined incorrespondence to a predetermined computation rule or based on acharacteristic field stored in the memory of the control apparatus.

In the next step 206, a check is made as to whether the determined fueltemperature lies above the previously determined critical temperaturethreshold. If this is not the case, then the program moves from step 206to step 207 wherein the decision is made that no hot-start situation ispresent. A hot-start bit, which is possibly provided in the controlapparatus, is not set in this case. In the next determination of theinjection duration, the normal injection time computation, which anywayruns in the control apparatus is used. Accordingly, no increase of thedetermined injection time by a so-called hot-start factor takes place.Thereafter, the method returns to step 202.

If, in contrast, it was determined in step 206 that the determined fueltemperature lies above the determined critical temperature then there isa movement over to step 209 wherein a decision is made as to a hot-startsituation. In step 209, a hot-start bit, which is present, for example,in the control apparatus, can be correspondingly set.

If a decision was made as to a hot-start in step 209, then the methodcontinues with step 210. In step 210, an increase factor for theinjection time, which is determined in the control apparatus, isdetermined under normal conditions in dependence upon to what extent thedetermined fuel temperature exceeded the critical temperature. In otherwords, in a hot-start situation, the injection duration is increased bya so-called hot-start factor. The hot-start factor is decisivelydependent upon the determined fuel temperature and the determinedcritical temperature and therefore indirectly decisively on the enginetemperature.

If the fuel temperature was the subject matter of discussion in theabove explanations, then it is presumed that the fuel temperature in ahigh-pressure store, for example, a common rail of a fuel supply systemis meant. The fuel temperature can either be determined directly via atemperature sensor 21 or via fuel temperature model 204.

1. A method for determining a first variable representing an injectionquantity in an internal combustion engine of a motor vehicle having afuel supply system, the method comprising the steps of: injecting fuelfrom a high-pressure region of said fuel supply system; determining ahot-start situation based on a second variable representing atemperature of said fuel and based on a pressure of said fuel; and, whensaid hot-start situation is detected, correcting said first variable independence upon said second variable.
 2. The method of claim 1, whereinsaid first variable is an injection duration.
 3. The method of claim 1,wherein said second variable is an engine temperature or a coolanttemperature.
 4. The method of claim 1, wherein the fuel pressure isdetermined in the high-pressure region of said fuel supply system.
 5. Acontrol apparatus for an internal combustion engine including aninternal combustion engine of a motor vehicle having a fuel supplysystem, the control apparatus comprising means for carrying out a methodfor determining a first variable representing an injection quantity insaid internal combustion engine, the method including the steps of:injecting fuel from a high-pressure region of said fuel supply system;determining a hot-start situation based on a second variablerepresenting a temperature of said fuel and based on a pressure of saidfuel; and, when said hot-start situation is detected, correcting saidfirst variable in dependence upon said second variable.
 6. A computerprogram comprising program-code means on a tangible medium for executingthe steps of a method for determining a first variable representing aninjection quantity in an internal combustion engine of a motor vehiclehaving a fuel supply system when said computer program is executed on acomputer including a control apparatus for said engine, the methodincluding the steps of: injecting fuel from a high-pressure region ofsaid fuel supply system; determining a hot-start situation based on asecond variable representing a temperature of said fuel and based on apressure of said fuel; and, when said hot-start situation is detected,correcting said first variable in dependence upon said second variable.7. A computer program product which comprises being stored on acomputer-readable data carrier for executing the steps of a method fordetermining a first variable representing an injection quantity in aninternal combustion engine of a motor vehicle having a fuel supplysystem when said computer program product is carried out on a computerincluding a control apparatus for said internal combustion engine, themethod including the steps of: injecting fuel from a high-pressureregion of said fuel supply system; determining a hot-start situationbased on a second variable representing a temperature of said fuel andbased on a pressure of said fuel; and, when said hot-start situation isdetected, correcting said first variable in dependence upon said secondvariable.
 8. An arrangement for determining a first variablerepresenting an injection quantity in an internal combustion engine of amotor vehicle having a fuel supply system, the arrangement comprising:means for injecting fuel from a high-pressure region of said fuel supplysystem; means for determining a hot-start situation based on a secondvariable representing a temperature of said fuel and based on a pressureof said fuel; and, when said hot-start situation is detected, means forcorrecting said first variable in dependence upon said second variable.